A novel parathyroid hormone (PTH) antagonist is proposed for the management and treatment of patients with hyperparathyroidism resulting from chronic renal failure. The specific aims of this research proposal include isolation and characterization of this antagonist from the serum-of patients with hyperparathyroidism. This natural antagonist is an N-truncated form of PTH. The isolation procedure will utilize immunoaffinity resins containing antibodies specific for the C-terminus and N-terminus of PTH. The purified protein will be tested for antagonist activity and its potency will be compared to current synthetic peptide antagonists. Identification of a physiological inhibitor of PTH from serum offers new opportunities in the design of therapeutic drugs for hyperparathyroidism. In addition, establishing the presence of functional PTH antagonists in the circulation may have a major impact on our understanding of the normal physiology and pathophysiology of PTH. PROPOSED COMMERCIAL APPLICATIONS: NOT AVAILABLE